PG exhibits a variety of important physiological activities in a trace amount. For its diversity, natural PG analogues and a vast number of derivatives thereof have been studied on synthesis and biological activities, with attempts to apply these compounds to pharmaceuticals. These studies are reported in many publications and Japanese Patent Application KOKAI No. 52-100446, Japanese Patent Application KOHYO No. 2-502009 (WO 89/00559), etc.
The compounds of the present invention are broadly covered by Formula I described in Japanese Patent Application KOHYO No. 2-502009 supra but there is no specific description on these compounds in the specification.
An object of the present invention is to provide compounds which possess much more potent pharmacological activities than PG derivatives known so far.